The present invention relates to magnetic recording systems. More particularly, the invention relates to magnetic head assemblies for use in such magnetic recording systems.
Magnetic recording systems wherein rigid magnetic recording media or magnetic disks are rotated adjacent to so-called "Winchester" type magnetic read/write heads which "fly" on an air bearing in very close proximity to the rigid magnetic disk are well known. Such systems are hereinafter sometimes referred to as "rigid disk systems". These rigid disk systems utilize noncontact magnetic retrieval and recording of data (i.e., read/write operation) and operate at very high speeds, typically at approximately 3600 rpm, which results in very high performance. The magnetic heads used in rigid disk systems are relatively inexpensive and have a relatively low mass, typically about 65 mg, as compared to heads utilized in other types of recording systems. Such low mass heads result in high efficiency in track to track access time and seek performance.
It might be explained here that the overall capacity or aerial density of magnetic data storage devices, in bits/sq. in., is equal to combination of track density (tracks/in.) and linear bit density (bits/in.). While rigid disk systems have high performance and exhibit relatively high track density, they exhibit less linear bit density than is possible with contact recording devices. Another disadvantage of rigid disk systems is so-called "head crashes", i.e., the head moving from its flying position over the record media into contact with the record media. Such head crashes can cause a loss of data because of damage to the record media and extensive down time because many times when a head crash occurs, damage is caused to the head/disk assembly (HDA) in the disk drive itself which must be repaired before the recording system can properly function again.
Magnetic recording systems which read and write data from flexible magnetic recording media have also been developed. In general, flexible recording media are less expensive than rigid recording media. Basically, such magnetic recording systems which utilize flexible recording media are of two types. In a first or conventional type of recording system, so called "floppy" disks and "floppy disk drives" are utilized. Floppy disk drives have been extensively used for small so-called microcomputer systems, for word-processing applications and the like. In these floppy disk systems, the floppy disk drive clamps the flexible disk onto a motor shaft which rotates the disk. The rotating disk, in turn, is contacted by a magnetic read/write head or two opposed magnetic read/write heads with the disk being sandwiched between the two heads. In order to assure contact between the magnetic head and the floppy disk and further, to assure proper read/write operation, heavy loading (approximately 10 grams) of the head or heads against the floppy disk or the use of pressure pads is required. Such heavy loading and the use of pressure pads requires low speed operation, typically about 1,000 rpm or less. Due to the "loaded contact" conditions of the floppy head/disk interface, the expected media life during single track dwell is approximately only 168 hours.
In theory, floppy disk systems can provide high linear density recording because the head is in contact with the media. This advantage is seldom utilized in practice because the slow rotational speed of the floppy drive precludes high performance, i.e. fast seek and track/track access times. Therefore the floppy drive has found a nitch market as a low performance, low capacity, and low cost drive. It is noteworthy that the floppy head is usually the expensive component of the floppy drive. The floppy head is more expensive than a rigid head due to its increased mass (approximately 150mg), multiple read/write and erase gaps, and multiple coil windings.
In a second type of recording system which uses flexible magnetic recording media, a floppy or flexible disk is rotated in close proximity to a flat rigid "Bernoulli" plate or surface. Such systems are hereinafter sometimes referred to as "Bernoulli systems". As is understood to those skilled in the art, the thin layer of air between the flexible disk and the Bernoulli plate or surface tends to rotate with the flexible disk and to be thrown outwardly by centrifugal force. This creates a negative pressure between the Bernoulli plate and the flexible disk which tends to pull the disk close to the plate and cause the disk to "fly" or become "stabilized" as these terms are used in the art, in a predictable planar relationship with respect to the Bernoulli surface. Essentially, an air bearing is created between the flexible magnetic disk and the rigid Bernoulli surface such that a constant and predictable spacing between the Bernoulli surface and the flexible magnetic disk is established. Once the flexible magnetic disk is stabilized, the magnetic head/coupler assembly utilized in these Bernoulli systems can be "coupled", as this term is used in the art, to the flexible magnetic disk. A magnetic head/coupler assembly which is coupled to the flexible disk will penetrate or dimple the flexible disk, i.e., the flexible recording media will substantially conform to or be shaped substantially to that of the magnetic head/coupler surface in the area of the record media which is located directly over the magnetic head/coupler. This dimpling phenomenon occurs directly over the magnetic head/coupler assembly and when effected, the flexible media "flies" with respect to the coupler and all points of the magnetic head/coupler assembly except for the area on the magnetic head called the "bearing". The bearing is centered over the read/write gap of the transducer or core and coil assembly of the magnetic head and contact between the flexible media and the magnetic head occurs in the bearing area.
In Bernoulli systems, the flexible magnetic media is rotated at a relatively high speed, typically about 2,000 rpm, and this results in high performance for such systems, i.e., higher performance than in floppy systems but lower than that of rigid disk systems. The cost of the magnetic head/coupler assembly utilized in Bernoulli system is relatively high as compared to the magnetic heads used in the rigid and the conventional floppy disk systems, i.e., they are more expensive than the heads utilized in these systems. The magnetic head/coupler assembly of Bernoulli systems has a very high mass, typically about 1300 mg. Therefore, to achieve respectable track to track access time, significantly greater power and actuator mass is required. With regard to aerial density or capacity, the Bernoulli systems have high linear bit density because they are contact type recording systems and they also use track following servos to achieve high track density. This results in high aerial density. Therefore Bernoulli systems can achieve equivalent or higher capacity than that of rigid disk systems and higher than the capacity achieved in practice by the conventional floppy systems which are also contact type recording systems. In Bernoulli systems, head crashes that cause loss of data and possible damage to the drive of the system are protected against because the record media generally flies beneath the head and would fall away from the head with any disruption. Consequently, Bernoulli systems are more rugged than rigid disk systems.
With the foregoing as background, it can be seen that it would be desirable to have a magnetic recording system with the advantages of the rigid systems, i.e., high performance, high track density, low cost recording heads, and low mass recording heads with attendant high track to track access time, as well as the advantages of the flexible systems, i.e., relatively inexpensive recording media and ruggedness as well as the relatively high linear bit density, along with high capacity of the Bernoulli systems.